Apparatus for collection of garden waste for use in the garden are well known. One type of device comprising an apparatus for collection of garden waste is a blower-vacuum device, commonly referred to as a “blowervac”. Blowervacs generally comprise a motor having an output shaft coupled to a fan. The motor is usually either petrol or electrically powered. The fan is usually enclosed within a volute. The fan is configured to draw air in along its axis of rotation and expel air out tangentially when the fan is driven by the motor. Fans having such a configuration are properly called centrifugal impellers. The exterior of the volute has a generally disc-shaped appearance. The volute is provided with both an air inlet generally aligned with the impeller's axis of rotation and at least one air outlet located at a point on the periphery of the volute. The interior of the volute is spiral-shaped to enable the flow of air generated by the fan in operation in the air inlet and out the air outlet. As their name implies, blowervacs have two modes of operation: blowing and vacuuming.
In the blowing mode of operation, clean air is drawn into the volute from the atmosphere via the air inlet thereto and is expelled via the air outlet. A blowing tube is attached to the air outlet in order to concentrate and direct the expelled air into a jet, which may be aimed in different directions by pointing the blowing tube as desired.
In the vacuuming mode of operation, garden waste may be collected up a vacuum tube connected to the blowervac in one of two ways, usually known as “clean fan” and “dirty fan” operation. In clean fan operation of a blowervac in vacuuming mode, clean air is drawn into the volute from the atmosphere via the air inlet thereto in the same manner as for blowing operation and the air expelled from the volute through the air outlet thereof is directed towards a collection device or receptacle.
Typically, the receptacle is porous to the passage of air therethrough and is also fed by the vacuum tube with air from ground level. Air passing into the receptacle from the volute therefore causes air to be sucked up the vacuum tube as well. Garden waste entrained with the air passing up the vacuum tube is collected in the receptacle without passing through the fan; hence, clean fan operation. In contrast, in dirty fan operation, an air-porous receptacle for garden waste is attached directly to the air outlet from the volute and the vacuum tube is instead attached to the air inlet thereto. In this latter case, air flow with entrained garden waste (i.e. dirty air flow) passes up the vacuum tube, enters the volute via the air inlet thereto and collides with the fan, before being expelled via the air outlet of the volute into the receptacle; hence, dirty fan operation. Collision of the garden waste with the fan causes the fan to mulch, or chop, the garden waste into smaller particles. Since garden waste mulched in this fashion contains far fewer air pockets than unmulched garden waste, the volume ratio of unmulched to mulched garden waste can be as much as 10:1. The garden waste receptacle can store a larger mass of garden waste in the same volume once it has been mulched than of unmulched waste.
A conventional blowervac providing dirty fan operation in the vacuuming mode thereof is described in U.S. Pat. No. 5,535,479 assigned to The Toro Company. FIG. 3 of U.S. Pat. No. 5,535,479 shows the blowervac thereof in the blowing mode of operation and FIG. 4 of this patent document shows the blowervac thereof in the vacuuming mode of operation with a dirty fan. The blowervac of U.S. Pat. No. 5,535,479 has an impeller permanently enclosed within a volute which may be used interchangeably with separable blowing and vacuum tubes.
A second conventional blowervac providing dirty fan operation in the vacuuming mode thereof is described in European patent publication No. 0 723 758 of Black & Decker Inc. FIG. 1 of EP 0 723 758 shows the blowervac thereof in the blowing mode of operation and FIG. 2 of this patent document shows the blowervac thereof in the vacuuming mode of operation with a dirty fan. FIG. 3 of this patent document shows an embodiment of the blowervac thereof convertible between a blowing mode of operation and a vacuuming mode of operation with a dirty fan. As may be seen from these three figures, the blowervac is provided with one or more different detachable volutes for use in the blowing and vacuuming modes of operation. The detachable volutes may be formed integrally with blowing and vacuum tubes as shown in FIGS. 1 and 2, respectively, of this document, or as a single detachable volute which may be used interchangeably with separable blowing and vacuum tubes as shown in FIG. 3. The blowervac of this patent document may be converted to clean fan operation in the vacuuming mode as is shown in FIG. 4 thereof.
The blowervacs of U.S. Pat. No. 5,535,479 and EP 0 723 758 suffer from certain disadvantages as follows. Firstly, the bag does not filter all the garden waste from the air because it allows some of it, particularly smaller sized matter such as dust, to pass through the wall of the bag to open atmosphere. This is a particular problem when the bag is located against, or in close proximity to, the body of a user. Garden waste, particularly dust, is expelled from the collection bag onto the body of the user, which is undesirable as it may dirty the user's clothing.
When the garden waste is wet, additional moisture is also able to pass through the walls of the bag, thus wetting the clothing of the user. If the moisture is mixed with some of the garden waste, such as dust, which is able to pass through the walls of the bag, it can stain the user's clothing.
The garden waste, particularly when wet, can clog the pores of the bag, thus reducing the porosity of the walls of the bag. This reduces the effectiveness of the collection bag as a filter and hence the performance of the device as a whole.
Another type of device comprising an apparatus for collection of garden waste is described in European patent publication No. 1 042 980 of Black & Decker Inc. FIG. 2 of EP 1 042 980 shows a vacuum cleaner for collection of garden waste which, unlike a blowervac, only has a vacuuming mode of operation. Air flows, together with entrained garden waste, along a vacuum tube in a direction indicated by Arrows A to an axial inlet of the fan having dirty fan operation. The fan mulches entrained garden waste and generates rotational movement of both the air and mulched garden waste about a toroidal chamber in a direction indicated by Arrows B. The garden waste is pushed by air flow away from the fan and along the length of the toroidal chamber in an axial direction indicated by Arrows C. The garden waste and some air flow enter a collection device equipped with an air return pipe to the vacuum tube. The remainder of the air flows through a toroidal outlet, also in the direction indicated by Arrows C.
The vacuum cleaner of EP 1 042 980 suffers from certain disadvantages as follows. The vacuum tube has a cross-sectional area which is large enough to suck garden waste such as leaves. The vacuum tube is surrounded by the toroidal air outlet which is surrounded by the toroidal chamber which, according to FIGS. 1 and 2, has an outer diameter approximately five times greater than that of the vacuum tube. This adds significant bulk to the device which makes it difficult to handle. Further, some of the air flow from the impeller is diverted towards a corner of the toroidal chamber from where its only escape is to the collection device via a small outlet duct. Restriction of air flow in this manner causes turbulence and increases energy losses. Also, the air flow is recycled, via the air return pipe, into the vacuum tube in case it re-entrains garden waste from the collection device. The recycled air flow reduces suction force at the tip of the vacuum tube which diminishes the device's ability to pick up new garden waste. Furthermore, air flow which is not so recycled is instead directed towards the tip of the vacuum tube. This further diminishes the device's ability to pick up garden waste by blowing it away from the tip of the vacuum tube.